The limiting reagent is the reactant present in the smallest stoichiometric amount, which is therefore completely consumed first and determines how much product can form. Once it runs out, the reaction stops, even if other reactants remain. The other reactants, present in relative excess, are left over when the reaction is complete.

限量试剂(限制反应物)是以最小化学计量量存在的反应物,因而最先被完全消耗,并决定能生成多少产物。一旦它耗尽,反应即停止,即使其他反应物仍有剩余。相对过量存在的其他反应物在反应结束时会剩下。